Probably ST ships use a forcefield setup to direct engine thrust and can redirect it forwards using this.. similar to the physical thrust reversers on aircraft.

It's a concept explored in a number of Sci-fi works. The SW EU for example calls it an "etheric rudder". But it's the same thing. Forcefields used to vector engine thrust in the desired direction.. including 180 degrees for reverse thrust.

...... (a) with the same amount of force (F) -- which, by Newton's second law, means reducing its inertial mass (m).

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There is no way that impulse engines can reduce mass for the Saucer section, or indeed, reduce mass for anything other than the exhaust gases produced by the impulse engines. I have the same manual, and I still don't see how you can get to your conclusion.

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It's right there in the words I quoted. It says outright that even the highest specific-impulse thrusters cannot accelerate a Galaxy-class ship fast enough. That tells you unambiguously that accelerating the exhaust to any speed is not going to impart enough acceleration by itself. If the driver coil does boost the acceleration to an effective degree, it therefore must be by some means other than accelerating the exhaust gases.

Also, it's elementary that reducing the mass of the exhaust gases would reduce thrust, not increase it. It's the equivalent of having a smaller amount of propellant, and there's no way less propellant equals more thrust. So I can't understand why you'd think that would be the intent. If you want higher acceleration, you need a higher ratio of propellant mass to vessel mass -- or, phrased another way, a lower ratio of vessel mass to propellant mass. Since there's no propulsive benefit in reducing the mass of the propellant, the intent can only be to reduce the mass of the vessel.

The driver coils are localised and specific to the fusion reactors that they are connected to. No connection to warp anything.

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Second part first: I never said they were connected to warp drive, except in the sense explicitly spelled out in the TM that they use a low-level warp field (i.e. below 1000 millicochranes and thus below the lightspeed threshold). You're reading things into my words that I'm not claiming.

As to the first part: The warp engines' driver coils are "localized" to the warp nacelles, but their field is large enough to encompass the entire ship and a surrounding "bubble" of space. Clearly such coils are able to have influence at a distance. It's just that the driver coils in the impulse engines are fewer in number and therefore less powerful; their effect can be just as broad but less intense, so that the spacetime distortion is not enough to create a warpfield but is sufficient to "flatten" the ship's gravity well and reduce its inertial mass.

Probably ST ships use a forcefield setup to direct engine thrust and can redirect it forwards using this.. similar to the physical thrust reversers on aircraft.

It's a concept explored in a number of Sci-fi works. The SW EU for example calls it an "etheric rudder". But it's the same thing. Forcefields used to vector engine thrust in the desired direction.. including 180 degrees for reverse thrust.

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Hey, that's a good idea. I hadn't thought of that, and I've had occasion to try to figure out how reverse impulse could work.

And ancient, where was the "air brakes" joke used in Futurama? I remember it from a Bugs Bunny cartoon, but not from there.

I agree with you on this one, the way starships move around does suggest the impulse drive is indeed a coil drive specialised to work at slower then light speeds, also it would explain the tremendoes acceleration and the little fuel it uses.

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We don't know how much fuel impulse engines require under normal circumstances, but if the NCC-1701 employs degenerate matter as reaction mass - say something like metallic hydrogen - it would to a certain extent explain, A). the Enterprise's on-screen performance for velocities < c, B). the apparent lack of fuel tanks that would otherwise take up ~99% of the vessel's interior volume, and C). the discrepancy between TMoST's 190,000 ton mass figure and Scotty's "almost a million gross tons of vessel" line in Mudd's Women.

This is one thing about Trek Tech that has always puzzled me. How do starships stop?

We know from the on-screen commands and actions that a ship at warp speed can translate to a sublight velocity within a few seconds. It is the slowing down from near light speed to a zero velocity that poses the problem.

The impulse engines all point in the wrong direction to be used for a retro-jet action and the Saucer and Battle section thrusters are used for station-keeping and fine maneuvering/attitude control of the ship.

I know that this aspect of Trek ships was considered and the idea of 'reverse thrusters' was mooted but the solution never went further than that throw-away idea and there is nothing in the Tech manual or elsewhere to suggest a method..

So, how does a Trek ship stop?

I have my own solution, but I am interested to hear other peoples ideas.

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Well, for warp drive (which is a reactionless, field-based system) that's something that happens as part of the "warp engine magic" so I'm guessing you're uninterested in that, and are really just concerned with the newtonian-flight model.

There are two main ways of looking at impulse among fandom. Some folks think it's also a "field-effect" system (that's non-canon but it can be argued from a science basis) while others think it's purely a newtonian thrust-based system. And a few, like me, think it's a combination of the two... using newtonian thrust inside of a "space-time bubble."

Well, for the TOS ship, the only engines we ever saw were the nacelles and the impulse deck (and to be fair, that was never defined, on-screen, as the impulse deck, nor were the nacelles ever officially described on-screen as the warp engines). This was by intent... MJ was given the direction to not ever define the technology too closely, but just to make it "look and feel real, but beyond our current abilities."

With the TMP ship, however, you have a lot more detail added, and there were not two, not three, but FOUR different "propulsion subsystems" on the 1701(r).

1) Warp Drive (in the nacelles)
2) Impulse drive (at the aft end of the saucer)
3) Reaction Control system (for orientation control, not for significant translational movement)
4) THRUSTERS.

Yes, it's that fourth one that people tend to forget (or to get confused with the RCS system or the impulse drive). But it was in the design.

If you have a model of the refit E, look closely at the spin of the secondary hull. There are four aft-facing cut-outs. Now, look at the forward edge, right adjacent to the deflector housing (on top). Four forward-facing cut-outs.

These are the thrusters... pure newtonian devices, essentially rocket engines used for low-speed manuevering. And this was always part of the design (remember in STVI... "thrusters ONLY, while in Spacedock")

SO...

1) perhaps it slows down purely using these.

Or,

2) perhaps it uses some vectoring "thrust reversers" on the impulse engines (either force-field based, or perhaps simply mechanical flaps we never saw).

Or,

3) Perhaps part of a planetary approach, which we never saw on-screen, involves the ship turning around and using its main impulse drive to slow itself (that's most likely in reality, I think, by the way)

Or,

4) Perhaps there are reverse engines behind panels someplace on the ship which we've also never seen (seems unlikely, but it's not impossible).

OR...

5) Perhaps they use some sort of field-effect "drag chute" which is somehow part of the subspace drive system (whether you think that's just warp drive, or if (like me) you think that subspace is also involved in "impulse" drive as its know in Treknology).

3) Reaction Control system (for orientation control, not for significant translational movement)

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I think it is safe to assume that roll, pitch and yaw maneuvers would be carried out with onboard momentum wheels and control moment gyros to minimize reaction mass consumption, just as it is done on present-day spacecraft on the order of, say, Lockheed Martin's A2100 Geosynchronous Satellite Bus.

Yes, it's that fourth one that people tend to forget (or to get confused with the RCS system or the impulse drive). But it was in the design.

If you have a model of the refit E, look closely at the spin of the secondary hull. There are four aft-facing cut-outs. Now, look at the forward edge, right adjacent to the deflector housing (on top). Four forward-facing cut-outs.

These are the thrusters... pure newtonian devices, essentially rocket engines used for low-speed manuevering. And this was always part of the design (remember in STVI... "thrusters ONLY, while in Spacedock")

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Who said thosethings are thrusters? Certainly not Andrew Probert. They aren't even indicated with that bright yellow color to warn dockyard workers of their presence a la the RCS packs.

4) Perhaps there are reverse engines behind panels someplace on the ship which we've also never seen (seems unlikely, but it's not impossible).

OR...

5) Perhaps they use some sort of field-effect "drag chute" which is somehow part of the subspace drive system (whether you think that's just warp drive, or if (like me) you think that subspace is also involved in "impulse" drive as its know in Treknology).

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I had a good laugh when you said there were parachutes or rather 'drag shutes'. LOL

Personally, I think the "drag chute" idea is among the most workable ones.

The following, while applying to the real world, might in fact be eminently untrue in the Trek universe:

And of course no starship ever "stops," it just matches velocity with some other object in space or goes into orbit of some other body. How much deceleration or course change is needed would depend on what the ship's velocity is relative to its destination or to the other vessel it's rendezvousing with.

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Rather than Newtonian speed being relative in the Trek universe, there could well be an absolute speed and an absolute stop in that universe. That is, the galaxy could have a static subspace framework of some sort in which ships could indeed dip their drag anchors, turning the symmetry of relativism into the pronounced asymmetry of absolute frames. Ships could decelerate by using this subspace anchor, but they couldn't accelerate by the same method, which is indeed the behavior we see.

Of course, since no dialogue specifically refers to subspace anchors (and we'd expect these devices to warrant dialogue at least once, when they fail at a dramatic moment to create tension!), it might be a good idea to claim that the subspace anchor function is performed by something in the impulse drives that isn't really a special component. Rather, the field reduction coils there might be automatic subspace anchors for all we know, perhaps always coupled to subspace by their material properties and thus dragging the ship down unless energized, but perhaps only doing the dragging when their field rapidly downramps (be it as the result of an "All stop!" command or a power failure).

Really, that's about the most realistic idea for describing Star Trek propulsion. Warp drive is just magic, impulse drive ignores Newtonian physics, antigravity has no clear rules. At least a drag chute -type device in space travel would meet the important criteria of not being slave to the rocket equation or the need to carry along the propellant required by Newtonian rules. It's not for nought that so much of the effort put into researching technologies for interstellar probes today is concentrated on sails...

Drag chutes aren't unique to Trek, of course. Larry Niven uses them in his Known Space, too, again with the idea of breaking the symmetry of relative motion. His version is a gravity anchor of sorts, using the mass of stars as the fixed reference frame. Such things could also work in the real world, doing "asymmetric velocity control" by hooking onto magnetic fields near planets so that the ship can then deploy a literal drag chute in the atmosphere. And by using the combination of light pressure and gravity from the Sun, two opposite forces, you get three-dee control of your motion without the need for propellant.

Really, that's about the most realistic idea for describing Star Trek propulsion. Warp drive is just magic, impulse drive ignores Newtonian physics, antigravity has no clear rules. At least a drag chute -type device in space travel would meet the important criteria of not being slave to the rocket equation or the need to carry along the propellant required by Newtonian rules. ........

(What is "wavey"?)

Timo Saloniemi

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"most realistic idea for describing Star Trek propulsion.", you have to be joking. Thats wind and sails technology, Larry Niven aside, the area of a 'chute' would have to be enormous and would only slow the vessel, not stop it dead.

Which, as said, is considerably more advanced and useful than rocketry in applications of interstellar propulsion, as understood by today's physics.

As for "stopping dead", there's no reason why a drag chute immersed in subspace wouldn't do that. After all, that's what aerodynamic chutes immersed in immobile air do today. And all we need anyway is slowing down enough that the motion isn't obvious in the scene; typically, leaving a few kilometers per second would do nicely in scenes that don't take place in low orbit...

It's not for nought that so much of the effort put into researching technologies for interstellar probes today is concentrated on sails...

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The navigational deflector field must generate drag against the interplanetary and interstellar media as an unavoidable byproduct of its intended function. Perhaps the resultant "virtual sail" may have braking applications in a sufficiently dense gas and dust medium, particularly if the deflector beam is "decollimated" to increase its apparent frontal area beyond the strict minimum required to protect the actual space vehicle from debris.

Quite possible. But it's not just the order-of-magnitude issue that turns me against this idea (space dust is a known and rather feeble quantity, subspace is a blissfully unknown one), it is my quest for an explanation that would fit the annoyingly plentiful evidence of "stopping due to power failure". Something "passive" must be at work there - and if it works that well in the power failure situations, it could just as well be assumed to be the mechanism behind all intentional braking as well.

Subspace drag anchors or restoring inertial mass to a ship that was originally artificially deprived of it are both essentially passive techniques. Moreover, both might work without the need for dedicated hardware and dialogue references thereto. But I guess it is always possible that an "active" technology is at work there instead, and that starships are carefully designed to activate this technology in case of impending power loss, using the last remains of power for an emergency surge of some sort.

Quite possible. But it's not just the order-of-magnitude issue that turns me against this idea (space dust is a known and rather feeble quantity, subspace is a blissfully unknown one)...

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The interstellar medium in the vicinity of Sol (aka the "Local Void") is ~0.1 particle per cubic centimeter, whereas the average for the Milky Way galaxy as a whole is ~1 particle per cc (see Local Interstellar Medium - IAU Colloquium #81 for more information). Depending on the maximum area of the deflector field, the resultant drag could save an appreciable amount of impulse reaction mass, particularly when decelerating from relativistic velocities. The actual calculations proving such a blithe assertion shall, of course, be left to the student to solve...

...it is my quest for an explanation that would fit the annoyingly plentiful evidence of "stopping due to power failure".

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If one may ask, did this ever explicitly happen in TOS or TAS?

Something "passive" must be at work there - and if it works that well in the power failure situations, it could just as well be assumed to be the mechanism behind all intentional braking as well.

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Or it can be ignored, depending upon your answer to the above question.

Subspace drag anchors or restoring inertial mass to a ship that was originally artificially deprived of it are both essentially passive techniques. Moreover, both might work without the need for dedicated hardware and dialogue references thereto. But I guess it is always possible that an "active" technology is at work there instead, and that starships are carefully designed to activate this technology in case of impending power loss, using the last remains of power for an emergency surge of some sort.

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My primary interest in Trek Tech is to discover - or, as a last resort, generate - as many parallels with real-world speculative astronautics as possible even at the (bargain) price of subverting franchise technical continuity, hence my grasping at straws.

3) Reaction Control system (for orientation control, not for significant translational movement)

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I think it is safe to assume that roll, pitch and yaw maneuvers would be carried out with onboard momentum wheels and control moment gyros to minimize reaction mass consumption, just as it is done on present-day spacecraft on the order of, say, Lockheed Martin's A2100 Geosynchronous Satellite Bus.

Yes, it's that fourth one that people tend to forget (or to get confused with the RCS system or the impulse drive). But it was in the design.

If you have a model of the refit E, look closely at the spin of the secondary hull. There are four aft-facing cut-outs. Now, look at the forward edge, right adjacent to the deflector housing (on top). Four forward-facing cut-outs.

These are the thrusters... pure newtonian devices, essentially rocket engines used for low-speed manuevering. And this was always part of the design (remember in STVI... "thrusters ONLY, while in Spacedock")

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Who said thosethings are thrusters? Certainly not Andrew Probert. They aren't even indicated with that bright yellow color to warn dockyard workers of their presence a la the RCS packs.

TGT

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Actually, Lee Cole said that they were thrusters. In the "official blueprints" which were released at the time of TMP. I'm surprised you've forgotten that.

I'm not aware of Andrew ever making a comment either way regarding those in any interview (or for that matter, on here). Andrew, if you're reading... care to comment?

But the 1979 TMP print set, done by Lee Cole, identified them as such, and fandom accepted that definition. It wasn't 'til TNG that there was ever any question about it, with that question raised when the 1701-D got similar features along its spine which were described (by Sternbach I believe, not Probert) as "fill ports." The thing is, there's no logic I can see to having fill ports designed in that fashion, facing directly aft, is there? Rick, if you're reading... feel free to comment as well, obviously!

But those pictures are great... and yes, those are the details I was talking about.

4) Perhaps there are reverse engines behind panels someplace on the ship which we've also never seen (seems unlikely, but it's not impossible).

OR...

5) Perhaps they use some sort of field-effect "drag chute" which is somehow part of the subspace drive system (whether you think that's just warp drive, or if (like me) you think that subspace is also involved in "impulse" drive as its know in Treknology).

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I had a good laugh when you said there were parachutes or rather 'drag shutes'. LOL

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Why "a good laugh?"

You'll note I didn't say "silk drag chute," I said "field effect 'drag chute'." Did you miss what this means, and envision a real physical parachute?